热处理对铸态镍铝青铜疲劳裂纹扩展速率的影响

Influence of Heat Treatment on Fatigue Crack Growth Rate of As-cast Nickel-Aluminum Bronze

对铸态镍铝青铜(NAB)进行了920℃正火和675℃退火热处理,研究了不同状态NAB的显微组织和拉伸性能;采用直流电压降(DCPD)法测试了其疲劳裂纹扩展速率,观察了裂纹扩展路径及疲劳断口形貌。结果表明:退火态与铸态试样的显微组织均由基体α相、残余β相以及三种Ni-Fe-Al金属间化合物相(κⅡ,κⅢ,κⅣ)组成,而正火态试样组织则由较多的残余β相以及均匀分布的κⅣ相组成,其强度更高但塑性明显降低;铸态试样的疲劳裂纹扩展速率最快,正火态试样的最慢;铸态和退火态试样中的疲劳裂纹在κ相相界处扩展,断裂方式主要为脆性解理断裂,而正火态试样的疲劳裂纹主要穿过α相扩展,断口出现了疲劳辉纹,且其疲劳裂纹扩展路径最为曲折。

The as-cast nickel-aluminum bronze （NAB） was normalized at 920 ℃ and annealed at 675 ℃ respectively, and then the microstructures and tensile properties of the NAB in different states were studied. The fatigue crack growth rates were measured by direct current potential drop （I）CPD） method and the fatigue crack growth path and fracture morphology were observed. The results show that the microstructures of the annealed and as-cast samples both consisted of α phase, residual β phase and three kinds of Ni-Fe-Al intermetallic compounds （κⅡ, κⅢ , κⅣ）, while that of the normalized sample consisted of residual β phase and evenly distributed κⅣ phase, which had a much higher strength and a decreased plasticity. The fatigue crack growth rate of the as-cast sample was the fastest while that of the normalized sample was the slowest. The fatigue crack in as-cast and annealed samples propagated from the interface of κ phases and showed a cleavage fracture mode; in normalized sample the fatigue crack propagated through α phase with fatigue striation on the fracture surface and the fatigue crack growth path was the most tortuose.